Google did the math, and they used the numbers. What everyone is saying is that numbers are useless without a model. Now, GReader caters to the needs of the 9% in the 90-9-1 rule[1], so you could never expect it to see huge numbers of adopters. Google did the math wrong, because they set the wrong expectation, based on a wrong popularity model, and they will indeed suffer.

[1] http://en.wikipedia.org/wiki/1%25_rule_%28Internet_culture%2...